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+# Copyright (c) Meta Platforms, Inc. and affiliates.
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+# This software may be used and distributed according to the terms of the Llama 2 Community License Agreement.
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+
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+import math
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+from dataclasses import dataclass
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+from typing import Optional, Tuple
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+
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+import fairscale.nn.model_parallel.initialize as fs_init
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+import torch
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+import torch.nn.functional as F
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+from fairscale.nn.model_parallel.layers import (
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+ ColumnParallelLinear,
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+ ParallelEmbedding,
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+ RowParallelLinear,
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+)
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+from torch import nn
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+
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+
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+@dataclass
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+class ModelArgs:
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+ dim: int = 4096
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+ n_layers: int = 32
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+ n_heads: int = 32
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+ n_kv_heads: Optional[int] = None
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+ vocab_size: int = -1 # defined later by tokenizer
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+ multiple_of: int = 256 # make SwiGLU hidden layer size multiple of large power of 2
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+ ffn_dim_multiplier: Optional[float] = None
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+ norm_eps: float = 1e-5
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+
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+ max_batch_size: int = 32
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+ max_seq_len: int = 2048
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+
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+
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+class RMSNorm(torch.nn.Module):
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+ def __init__(self, dim: int, eps: float = 1e-6):
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+ """
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+ Initialize the RMSNorm normalization layer.
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+
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+ Args:
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+ dim (int): The dimension of the input tensor.
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+ eps (float, optional): A small value added to the denominator for numerical stability. Default is 1e-6.
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+
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+ Attributes:
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+ eps (float): A small value added to the denominator for numerical stability.
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+ weight (nn.Parameter): Learnable scaling parameter.
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+
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+ """
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+ super().__init__()
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+ self.eps = eps
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+ self.weight = nn.Parameter(torch.ones(dim))
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+
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+ def _norm(self, x):
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+ """
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+ Apply the RMSNorm normalization to the input tensor.
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+
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+ Args:
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+ x (torch.Tensor): The input tensor.
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+
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+ Returns:
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+ torch.Tensor: The normalized tensor.
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+
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+ """
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+ return x * torch.rsqrt(x.pow(2).mean(-1, keepdim=True) + self.eps)
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+
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+ def forward(self, x):
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+ """
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+ Forward pass through the RMSNorm layer.
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+
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+ Args:
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+ x (torch.Tensor): The input tensor.
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+
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+ Returns:
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+ torch.Tensor: The output tensor after applying RMSNorm.
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+
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+ """
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+ output = self._norm(x.float()).type_as(x)
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+ return output * self.weight
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+
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+
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+def precompute_freqs_cis(dim: int, end: int, theta: float = 10000.0):
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+ """
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+ Precompute the frequency tensor for complex exponentials (cis) with given dimensions.
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+
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+ This function calculates a frequency tensor with complex exponentials using the given dimension 'dim'
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+ and the end index 'end'. The 'theta' parameter scales the frequencies.
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+ The returned tensor contains complex values in complex64 data type.
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+
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+ Args:
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+ dim (int): Dimension of the frequency tensor.
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+ end (int): End index for precomputing frequencies.
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+ theta (float, optional): Scaling factor for frequency computation. Defaults to 10000.0.
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+
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+ Returns:
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+ torch.Tensor: Precomputed frequency tensor with complex exponentials.
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+
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+
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+
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+
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+ """
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+ freqs = 1.0 / (theta ** (torch.arange(0, dim, 2)[: (dim // 2)].float() / dim))
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+ t = torch.arange(end, device=freqs.device) # type: ignore
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+ freqs = torch.outer(t, freqs).float() # type: ignore
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+ freqs_cis = torch.polar(torch.ones_like(freqs), freqs) # complex64
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+ return freqs_cis
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+
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+
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+def reshape_for_broadcast(freqs_cis: torch.Tensor, x: torch.Tensor):
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+ """
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+ Reshape frequency tensor for broadcasting it with another tensor.
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+
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+ This function reshapes the frequency tensor to have the same shape as the target tensor 'x'
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+ for the purpose of broadcasting the frequency tensor during element-wise operations.
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+
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+ Args:
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+ freqs_cis (torch.Tensor): Frequency tensor to be reshaped.
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+ x (torch.Tensor): Target tensor for broadcasting compatibility.
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+
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+ Returns:
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+ torch.Tensor: Reshaped frequency tensor.
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+
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+ Raises:
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+ AssertionError: If the frequency tensor doesn't match the expected shape.
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+ AssertionError: If the target tensor 'x' doesn't have the expected number of dimensions.
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+ """
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+ ndim = x.ndim
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+ assert 0 <= 1 < ndim
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+ assert freqs_cis.shape == (x.shape[1], x.shape[-1])
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+ shape = [d if i == 1 or i == ndim - 1 else 1 for i, d in enumerate(x.shape)]
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+ return freqs_cis.view(*shape)
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+
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+
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+def apply_rotary_emb(
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+ xq: torch.Tensor,
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+ xk: torch.Tensor,
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+ freqs_cis: torch.Tensor,
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+) -> Tuple[torch.Tensor, torch.Tensor]:
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+ """
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+ Apply rotary embeddings to input tensors using the given frequency tensor.
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+
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+ This function applies rotary embeddings to the given query 'xq' and key 'xk' tensors using the provided
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+ frequency tensor 'freqs_cis'. The input tensors are reshaped as complex numbers, and the frequency tensor
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+ is reshaped for broadcasting compatibility. The resulting tensors contain rotary embeddings and are
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+ returned as real tensors.
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+
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+ Args:
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+ xq (torch.Tensor): Query tensor to apply rotary embeddings.
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+ xk (torch.Tensor): Key tensor to apply rotary embeddings.
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+ freqs_cis (torch.Tensor): Precomputed frequency tensor for complex exponentials.
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+
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+ Returns:
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+ Tuple[torch.Tensor, torch.Tensor]: Tuple of modified query tensor and key tensor with rotary embeddings.
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+
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+
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+
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+ """
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+ xq_ = torch.view_as_complex(xq.float().reshape(*xq.shape[:-1], -1, 2))
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+ xk_ = torch.view_as_complex(xk.float().reshape(*xk.shape[:-1], -1, 2))
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+ freqs_cis = reshape_for_broadcast(freqs_cis, xq_)
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+ xq_out = torch.view_as_real(xq_ * freqs_cis).flatten(3)
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+ xk_out = torch.view_as_real(xk_ * freqs_cis).flatten(3)
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+ return xq_out.type_as(xq), xk_out.type_as(xk)
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+
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+
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+def repeat_kv(x: torch.Tensor, n_rep: int) -> torch.Tensor:
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+ """torch.repeat_interleave(x, dim=2, repeats=n_rep)"""
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+ bs, slen, n_kv_heads, head_dim = x.shape
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+ if n_rep == 1:
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+ return x
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+ return (
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+ x[:, :, :, None, :]
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+ .expand(bs, slen, n_kv_heads, n_rep, head_dim)
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+ .reshape(bs, slen, n_kv_heads * n_rep, head_dim)
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+ )
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+
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+
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+class Attention(nn.Module):
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+ """Multi-head attention module."""
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+ def __init__(self, args: ModelArgs):
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+ """
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+ Initialize the Attention module.
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+
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+ Args:
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+ args (ModelArgs): Model configuration parameters.
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+
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+ Attributes:
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+ n_kv_heads (int): Number of key and value heads.
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+ n_local_heads (int): Number of local query heads.
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+ n_local_kv_heads (int): Number of local key and value heads.
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+ n_rep (int): Number of repetitions for local heads.
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+ head_dim (int): Dimension size of each attention head.
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+ wq (ColumnParallelLinear): Linear transformation for queries.
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+ wk (ColumnParallelLinear): Linear transformation for keys.
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+ wv (ColumnParallelLinear): Linear transformation for values.
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+ wo (RowParallelLinear): Linear transformation for output.
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+ cache_k (torch.Tensor): Cached keys for attention.
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+ cache_v (torch.Tensor): Cached values for attention.
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+
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+ """
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+ super().__init__()
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+ self.n_kv_heads = args.n_heads if args.n_kv_heads is None else args.n_kv_heads
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+ model_parallel_size = fs_init.get_model_parallel_world_size()
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+ self.n_local_heads = args.n_heads // model_parallel_size
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+ self.n_local_kv_heads = self.n_kv_heads // model_parallel_size
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+ self.n_rep = self.n_local_heads // self.n_local_kv_heads
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+ self.head_dim = args.dim // args.n_heads
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+
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+ self.wq = ColumnParallelLinear(
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+ args.dim,
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+ args.n_heads * self.head_dim,
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+ bias=False,
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+ gather_output=False,
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+ init_method=lambda x: x,
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+ )
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+ self.wk = ColumnParallelLinear(
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+ args.dim,
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+ self.n_kv_heads * self.head_dim,
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+ bias=False,
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+ gather_output=False,
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+ init_method=lambda x: x,
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+ )
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+ self.wv = ColumnParallelLinear(
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+ args.dim,
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+ self.n_kv_heads * self.head_dim,
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+ bias=False,
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+ gather_output=False,
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+ init_method=lambda x: x,
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+ )
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+ self.wo = RowParallelLinear(
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+ args.n_heads * self.head_dim,
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+ args.dim,
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+ bias=False,
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+ input_is_parallel=True,
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+ init_method=lambda x: x,
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+ )
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+
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+ self.cache_k = torch.zeros(
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+ (
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+ args.max_batch_size,
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+ args.max_seq_len,
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+ self.n_local_kv_heads,
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+ self.head_dim,
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+ )
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+ ).cuda()
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+ self.cache_v = torch.zeros(
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+ (
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+ args.max_batch_size,
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+ args.max_seq_len,
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+ self.n_local_kv_heads,
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+ self.head_dim,
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+ )
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+ ).cuda()
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+
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+ def forward(
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+ self,
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+ x: torch.Tensor,
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+ start_pos: int,
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+ freqs_cis: torch.Tensor,
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+ mask: Optional[torch.Tensor],
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+ ):
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+ """
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+ Forward pass of the attention module.
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+
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+ Args:
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+ x (torch.Tensor): Input tensor.
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+ start_pos (int): Starting position for caching.
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+ freqs_cis (torch.Tensor): Precomputed frequency tensor.
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+ mask (torch.Tensor, optional): Attention mask tensor.
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+
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+ Returns:
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+ torch.Tensor: Output tensor after attention.
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+
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+ """
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+ bsz, seqlen, _ = x.shape
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+ xq, xk, xv = self.wq(x), self.wk(x), self.wv(x)
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+
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+ xq = xq.view(bsz, seqlen, self.n_local_heads, self.head_dim)
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+ xk = xk.view(bsz, seqlen, self.n_local_kv_heads, self.head_dim)
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+ xv = xv.view(bsz, seqlen, self.n_local_kv_heads, self.head_dim)
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+
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+ xq, xk = apply_rotary_emb(xq, xk, freqs_cis=freqs_cis)
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+
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+ self.cache_k = self.cache_k.to(xq)
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+ self.cache_v = self.cache_v.to(xq)
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+
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+ self.cache_k[:bsz, start_pos : start_pos + seqlen] = xk
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+ self.cache_v[:bsz, start_pos : start_pos + seqlen] = xv
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+
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+ keys = self.cache_k[:bsz, : start_pos + seqlen]
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+ values = self.cache_v[:bsz, : start_pos + seqlen]
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+
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+ # repeat k/v heads if n_kv_heads < n_heads
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+ keys = repeat_kv(keys, self.n_rep) # (bs, cache_len + seqlen, n_local_heads, head_dim)
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+ values = repeat_kv(values, self.n_rep) # (bs, cache_len + seqlen, n_local_heads, head_dim)
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+
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+ xq = xq.transpose(1, 2) # (bs, n_local_heads, seqlen, head_dim)
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+ keys = keys.transpose(1, 2) # (bs, n_local_heads, cache_len + seqlen, head_dim)
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+ values = values.transpose(1, 2) # (bs, n_local_heads, cache_len + seqlen, head_dim)
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+ scores = torch.matmul(xq, keys.transpose(2, 3)) / math.sqrt(self.head_dim)
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+ if mask is not None:
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+ scores = scores + mask # (bs, n_local_heads, seqlen, cache_len + seqlen)
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+ scores = F.softmax(scores.float(), dim=-1).type_as(xq)
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+ output = torch.matmul(scores, values) # (bs, n_local_heads, seqlen, head_dim)
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+ output = output.transpose(1, 2).contiguous().view(bsz, seqlen, -1)
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+ return self.wo(output)
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+
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+
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+class FeedForward(nn.Module):
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+ def __init__(
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+ self,
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+ dim: int,
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+ hidden_dim: int,
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+ multiple_of: int,
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+ ffn_dim_multiplier: Optional[float],
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+ ):
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+ """
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+ Initialize the FeedForward module.
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+
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+ Args:
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+ dim (int): Input dimension.
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+ hidden_dim (int): Hidden dimension of the feedforward layer.
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+ multiple_of (int): Value to ensure hidden dimension is a multiple of this value.
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+ ffn_dim_multiplier (float, optional): Custom multiplier for hidden dimension. Defaults to None.
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+
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+ Attributes:
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+ w1 (ColumnParallelLinear): Linear transformation for the first layer.
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+ w2 (RowParallelLinear): Linear transformation for the second layer.
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+ w3 (ColumnParallelLinear): Linear transformation for the third layer.
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+
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+ """
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+ super().__init__()
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+ hidden_dim = int(2 * hidden_dim / 3)
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+ # custom dim factor multiplier
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+ if ffn_dim_multiplier is not None:
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+ hidden_dim = int(ffn_dim_multiplier * hidden_dim)
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+ hidden_dim = multiple_of * ((hidden_dim + multiple_of - 1) // multiple_of)
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+
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+ self.w1 = ColumnParallelLinear(
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+ dim, hidden_dim, bias=False, gather_output=False, init_method=lambda x: x
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|
|
+ )
|
|
|
|
+ self.w2 = RowParallelLinear(
|
|
|
|
+ hidden_dim, dim, bias=False, input_is_parallel=True, init_method=lambda x: x
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|
|
|
+ )
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|
|
|
+ self.w3 = ColumnParallelLinear(
|
|
|
|
+ dim, hidden_dim, bias=False, gather_output=False, init_method=lambda x: x
|
|
|
|
+ )
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|
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|
+
|
|
|
|
+ def forward(self, x):
|
|
|
|
+ return self.w2(F.silu(self.w1(x)) * self.w3(x))
|
|
|
|
+
|
|
|
|
+
|
|
|
|
+class TransformerBlock(nn.Module):
|
|
|
|
+ def __init__(self, layer_id: int, args: ModelArgs):
|
|
|
|
+ """
|
|
|
|
+ Initialize a TransformerBlock.
|
|
|
|
+
|
|
|
|
+ Args:
|
|
|
|
+ layer_id (int): Identifier for the layer.
|
|
|
|
+ args (ModelArgs): Model configuration parameters.
|
|
|
|
+
|
|
|
|
+ Attributes:
|
|
|
|
+ n_heads (int): Number of attention heads.
|
|
|
|
+ dim (int): Dimension size of the model.
|
|
|
|
+ head_dim (int): Dimension size of each attention head.
|
|
|
|
+ attention (Attention): Attention module.
|
|
|
|
+ feed_forward (FeedForward): FeedForward module.
|
|
|
|
+ layer_id (int): Identifier for the layer.
|
|
|
|
+ attention_norm (RMSNorm): Layer normalization for attention output.
|
|
|
|
+ ffn_norm (RMSNorm): Layer normalization for feedforward output.
|
|
|
|
+
|
|
|
|
+ """
|
|
|
|
+ super().__init__()
|
|
|
|
+ self.n_heads = args.n_heads
|
|
|
|
+ self.dim = args.dim
|
|
|
|
+ self.head_dim = args.dim // args.n_heads
|
|
|
|
+ self.attention = Attention(args)
|
|
|
|
+ self.feed_forward = FeedForward(
|
|
|
|
+ dim=args.dim,
|
|
|
|
+ hidden_dim=4 * args.dim,
|
|
|
|
+ multiple_of=args.multiple_of,
|
|
|
|
+ ffn_dim_multiplier=args.ffn_dim_multiplier,
|
|
|
|
+ )
|
|
|
|
+ self.layer_id = layer_id
|
|
|
|
+ self.attention_norm = RMSNorm(args.dim, eps=args.norm_eps)
|
|
|
|
+ self.ffn_norm = RMSNorm(args.dim, eps=args.norm_eps)
|
|
|
|
+
|
|
|
|
+ def forward(
|
|
|
|
+ self,
|
|
|
|
+ x: torch.Tensor,
|
|
|
|
+ start_pos: int,
|
|
|
|
+ freqs_cis: torch.Tensor,
|
|
|
|
+ mask: Optional[torch.Tensor],
|
|
|
|
+ ):
|
|
|
|
+ """
|
|
|
|
+ Perform a forward pass through the TransformerBlock.
|
|
|
|
+
|
|
|
|
+ Args:
|
|
|
|
+ x (torch.Tensor): Input tensor.
|
|
|
|
+ start_pos (int): Starting position for attention caching.
|
|
|
|
+ freqs_cis (torch.Tensor): Precomputed cosine and sine frequencies.
|
|
|
|
+ mask (torch.Tensor, optional): Masking tensor for attention. Defaults to None.
|
|
|
|
+
|
|
|
|
+ Returns:
|
|
|
|
+ torch.Tensor: Output tensor after applying attention and feedforward layers.
|
|
|
|
+
|
|
|
|
+ """
|
|
|
|
+ h = x + self.attention.forward(
|
|
|
|
+ self.attention_norm(x), start_pos, freqs_cis, mask
|
|
|
|
+ )
|
|
|
|
+ out = h + self.feed_forward.forward(self.ffn_norm(h))
|
|
|
|
+ return out
|
|
|
|
+
|
|
|
|
+
|
|
|
|
+class Transformer(nn.Module):
|
|
|
|
+ def __init__(self, params: ModelArgs):
|
|
|
|
+ """
|
|
|
|
+ Initialize a Transformer model.
|
|
|
|
+
|
|
|
|
+ Args:
|
|
|
|
+ params (ModelArgs): Model configuration parameters.
|
|
|
|
+
|
|
|
|
+ Attributes:
|
|
|
|
+ params (ModelArgs): Model configuration parameters.
|
|
|
|
+ vocab_size (int): Vocabulary size.
|
|
|
|
+ n_layers (int): Number of layers in the model.
|
|
|
|
+ tok_embeddings (ParallelEmbedding): Token embeddings.
|
|
|
|
+ layers (torch.nn.ModuleList): List of Transformer blocks.
|
|
|
|
+ norm (RMSNorm): Layer normalization for the model output.
|
|
|
|
+ output (ColumnParallelLinear): Linear layer for final output.
|
|
|
|
+ freqs_cis (torch.Tensor): Precomputed cosine and sine frequencies.
|
|
|
|
+
|
|
|
|
+ """
|
|
|
|
+ super().__init__()
|
|
|
|
+ self.params = params
|
|
|
|
+ self.vocab_size = params.vocab_size
|
|
|
|
+ self.n_layers = params.n_layers
|
|
|
|
+
|
|
|
|
+ self.tok_embeddings = ParallelEmbedding(
|
|
|
|
+ params.vocab_size, params.dim, init_method=lambda x: x
|
|
|
|
+ )
|
|
|
|
+
|
|
|
|
+ self.layers = torch.nn.ModuleList()
|
|
|
|
+ for layer_id in range(params.n_layers):
|
|
|
|
+ self.layers.append(TransformerBlock(layer_id, params))
|
|
|
|
+
|
|
|
|
+ self.norm = RMSNorm(params.dim, eps=params.norm_eps)
|
|
|
|
+ self.output = ColumnParallelLinear(
|
|
|
|
+ params.dim, params.vocab_size, bias=False, init_method=lambda x: x
|
|
|
|
+ )
|
|
|
|
+
|
|
|
|
+ self.freqs_cis = precompute_freqs_cis(
|
|
|
|
+ # Note that self.params.max_seq_len is multiplied by 2 because the token limit for the Llama 2 generation of models is 4096.
|
|
|
|
+ # Adding this multiplier instead of using 4096 directly allows for dynamism of token lengths while training or fine-tuning.
|
|
|
|
+ self.params.dim // self.params.n_heads, self.params.max_seq_len * 2
|
|
|
|
+ )
|
|
|
|
+
|
|
|
|
+ @torch.inference_mode()
|
|
|
|
+ def forward(self, tokens: torch.Tensor, start_pos: int):
|
|
|
|
+ """
|
|
|
|
+ Perform a forward pass through the Transformer model.
|
|
|
|
+
|
|
|
|
+ Args:
|
|
|
|
+ tokens (torch.Tensor): Input token indices.
|
|
|
|
+ start_pos (int): Starting position for attention caching.
|
|
|
|
+
|
|
|
|
+ Returns:
|
|
|
|
+ torch.Tensor: Output logits after applying the Transformer model.
|
|
|
|
+
|
|
|
|
+ """
|
|
|
|
+ _bsz, seqlen = tokens.shape
|
|
|
|
+ h = self.tok_embeddings(tokens)
|
|
|
|
+ self.freqs_cis = self.freqs_cis.to(h.device)
|
|
|
|
+ freqs_cis = self.freqs_cis[start_pos : start_pos + seqlen]
|
|
|
|
+
|
|
|
|
+ mask = None
|
|
|
|
+ if seqlen > 1:
|
|
|
|
+ mask = torch.full(
|
|
|
|
+ (seqlen, seqlen), float("-inf"), device=tokens.device
|
|
|
|
+ )
|
|
|
|
+
|
|
|
|
+ mask = torch.triu(mask, diagonal=1)
|
|
|
|
+
|
|
|
|
+ # When performing key-value caching, we compute the attention scores
|
|
|
|
+ # only for the new sequence. Thus, the matrix of scores is of size
|
|
|
|
+ # (seqlen, cache_len + seqlen), and the only masked entries are (i, j) for
|
|
|
|
+ # j > cache_len + i, since row i corresponds to token cache_len + i.
|
|
|
|
+ mask = torch.hstack([
|
|
|
|
+ torch.zeros((seqlen, start_pos), device=tokens.device),
|
|
|
|
+ mask
|
|
|
|
+ ]).type_as(h)
|
|
|
|
+
|
|
|
|
+ for layer in self.layers:
|
|
|
|
+ h = layer(h, start_pos, freqs_cis, mask)
|
|
|
|
+ h = self.norm(h)
|
|
|
|
+ output = self.output(h).float()
|
|
|
|
+ return output
|